In recent years, in order to improve fuel saving performance without reducing power performance of a vehicle, a so-called downsizing concept has been applied to an engine with a supercharger to maintain power performance by supercharging by the supercharger, while improving fuel economy by making an exhaust amount of the engine smaller.
With this engine with the supercharger, since fresh air of a high temperature and high pressure, which is compressed by the supercharger, is taken into a combustion chamber, a cylinder inner pressure or a cylinder temperature easily become high compared to a naturally aspirated engine, and a so-called pre-ignition (abnormal combustion) in which an air fuel mixture in the combustion chamber spontaneously ignites before an ignition timing of the cylinder easily occurs. Once pre-ignition occurs, not only are noises or vibrations associated with sharply increasing the cylinder inner pressure generated, but also causing damage to the engine is possible due to continuous pre-ignition.
Therefore, early detection of pre-ignition and suppression of an occurrence of pre-ignition have been considered. For example, in a pre-ignition detection device described in Patent Document 1, pre-ignition is certainly detectable by determining that pre-ignition occurred when a difference between a timing when the occurrence of abnormal vibrations was detected and an ignition timing is equal to or less than a predetermined value. Moreover, according to Patent Document 2, in an operation range of a low rotation and a high load in which knocking easily occurs, since the time from the principal fuel injection of a compression stroke to the ignition timing is kept short by injecting a small amount of fuel during an intake stroke and injecting the remaining fuel (principal fuel injection) during the compression stroke, the possibility to avoid the occurrence of pre-ignition is indicated. Additionally, in a cylinder-direct-injection type internal combustion engine described in Patent Document 2, when the occurrence of pre-ignition is not detected or predicted, the fuel injection is performed in the intake stroke, and only when the occurrence of pre-ignition is detected or predicted, pre-ignition is avoided by retarding the fuel injection timing to the compression stroke.